Date of Award

Winter 2017

Project Type

Thesis

Program or Major

Biochemistry

Degree Name

Master of Science

First Advisor

Cheryl A Whistler

Second Advisor

Estelle Hrabak

Third Advisor

Krisztina Varga

Abstract

Prokaryotes encode a remarkable ability to adapt to niches by sensing environmental cues through signal transduction systems (STSs). Typical STS proteins interact through a phosphorylation relay between histidine (His) and aspartate (Asp) residues within modular domains on sensory kinase and response regulator (RR) proteins to elicit cellular responses. A single point mutation in the sensor kinase BinK (BinK1 R537C) conferred an outstanding ability for the non-native V. fischeri strain MJ11 to successfully colonize Euprymna scolopes by affecting multiple symbiotic phenotypes including luminescence activation. However, the role of BinK in luminescence, the interacting partners, and functional mechanism are unknown. We hypothesized that BinK interacts upstream of an orphaned RR and acts as a canonical sensor kinase using a C-terminal receiver (REC) domain to activate luminescence. Heterologous multi-copy expression of BinK in native V. fischeri strain ES114 demonstrated that BinK does not utilize an orphan RR, but instead interfaces with the LuxU-LuxO node to activate luminescence. Additionally, BinK with a truncated REC domain and a REC domain with an aspartate – alanine substitution abolished luminescence activation where the level of light emitted matched the level of light emitted by a strain harboring the empty vector plasmid, suggesting BinK activates luminescence in a REC-dependent manner using the conserved Asp residue for suspected phosphatase / dephosphorylation activity. Elimination of the kinase / auto-phosphorylation activity of the HisKA domain by incorporating a histidine – glutamine substitution did not alter BinK luminescence activation. Though these findings demonstrate one mechanism by which BinK activates luminescence, it is still not clear how the evolved binK1 R537C mutation in the HATPase catalytic domain, a domain important in kinase function, influences REC-dependent dephosphorylation. By using multi-copy expression, BinK1 reduces luminescence and increases qrr1 expression, and like BinK, works in a REC-dependent manner. These data suggest that one way BinK1 conferred the jump to symbiosis was through reduced or altered function. Furthermore, this mutation unveiled BinK as another potential regulator in bioluminescence where it is poised to work in a manner similar to quorum sensing activators AinR and LuxQ to activate luminescence.

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